//! TrueType bytecode interpreter — executes font programs (fpgm, prep) and

//! per-glyph instructions to grid-fit outlines.

//!

//! # Specification references

//!

//! - **MS OpenType**: <https://learn.microsoft.com/en-us/typography/opentype/spec/tt_instructions>

//! - **Apple TrueType RM**: <https://developer.apple.com/fonts/TrueType-Reference-Manual/RM05/Chap5.html>

//!

//! # Key instructions

//!

//! | Opcode | Name   | Description |

//! |--------|--------|-------------|

//! | 0x2E   | MDAP   | Move Direct Absolute Point (touch + optional round) |

//! | 0x3E   | MIAP   | Move Indirect Absolute Point (CVT-based, key for twilight zone init) |

//! | 0xC0+  | MDRP   | Move Direct Relative Point (measured original distance) |

//! | 0xE0+  | MIRP   | Move Indirect Relative Point (CVT-based distance from reference) |

//! | 0x39   | IP     | Interpolate Point (preserve relative position between rp1/rp2) |

//! | 0x30   | IUP    | Interpolate Untouched Points (final pass, per-contour) |

//! | 0x5D+  | DELTAP | Delta Exception Point (ppem-specific pixel tuning) |

//! | 0x73+  | DELTAC | Delta Exception CVT (ppem-specific CVT modification) |

//!

//! # Twilight zone (zone 0)

//!

//! The `prep` program uses MIAP on zone 0 to create reference points that

//! encode key font measurements (cap height, x-height, stem widths, etc.).

//! These points must be properly initialized (original + current coordinates)

//! so that glyph programs can reference them via MIRP/IP for grid-fitting.

use std::fmt;

use super::f26dot6::{compute_scale, F2Dot14, F26Dot6};

use super::graphics_state::{GraphicsState, RoundState};

// ── Error type ───────────────────────────────────────────────────────

#[derive(Clone, Debug, PartialEq, Eq)]

pub enum HintError {

    StackOverflow,

    StackUnderflow,

    InvalidOpcode(u8),

    UndefinedFunction(u32),

    CallStackOverflow,

    InvalidPointIndex(u32),

    InvalidCvtIndex(u32),

    InvalidStorageIndex(u32),

    InvalidZone(u32),

    DivideByZero,

    UnexpectedEndOfBytecode,

    InvalidJump,

    ExceededMaxInstructions,

    FontNotReady,

}

impl fmt::Display for HintError {

            }

            }

            }

            HintError::UnexpectedEndOfBytecode => {

            }

            HintError::ExceededMaxInstructions => {

            }

        }

}

impl std::error::Error for HintError {}

// ── FreeType-compatible signed multiply-divide ──────────────────────

//

// Matches FreeType's `FT_MulDiv`: compute `a * b / c` with correct

// rounding for any sign combination.  The trick is to take absolute

// values, add a half-divisor for rounding, divide, then reapply sign.

#[inline]

/// FreeType's FT_DivFix: compute `(a << 16) / b` with signed rounding.

/// Returns a 16.16 fixed-point scale factor.

#[inline]

/// FreeType's FT_MulFix: compute `(a * b + 0x8000) >> 16` with signed rounding.

/// Multiplies a value by a 16.16 fixed-point factor.

#[inline]

// ── Point / Zone types ───────────────────────────────────────────────

#[derive(Copy, Clone, Debug, Default)]

pub struct Point {

    pub x: i32, // F26Dot6

    pub y: i32, // F26Dot6

}

bitflags::bitflags! {

    #[derive(Copy, Clone, Debug, Default)]

    pub struct PointFlags: u8 {

        const TOUCHED_X = 0x01;

        const TOUCHED_Y = 0x02;

        const ON_CURVE  = 0x04;

    }

}

#[derive(Clone, Debug)]

pub struct Zone {

    pub original: Vec<Point>,

    pub current: Vec<Point>,

    /// Unscaled original coordinates in font units (FreeType's "orus").

    /// Used by IUP for more precise interpolation — integer font-unit

    /// coordinates avoid the rounding errors present in scaled F26Dot6.

    pub orus: Vec<Point>,

    pub flags: Vec<PointFlags>,

    pub contour_ends: Vec<u16>,

}

impl Zone {

    /// Ensure the zone can hold at least `n` points, growing if necessary.

    #[inline]

}

// ── Function definition ──────────────────────────────────────────────

#[derive(Clone, Debug)]

pub struct FuncDef {

    pub bytecode: Vec<u8>,

}

// ── Maximum instruction count to prevent infinite loops ──────────────

const MAX_INSTRUCTIONS: u64 = 1_000_000;

const MAX_CALL_DEPTH: u32 = 64;

// ── Interpreter ──────────────────────────────────────────────────────

#[derive(Clone, Debug)]

pub struct Interpreter {

    // Stack

    pub(crate) stack: Vec<i32>,

    max_stack: usize,

    // CVT (F26Dot6 values stored as i32)

    pub(crate) cvt: Vec<i32>,

    // Original scaled CVT values (before prep/WCVTP modifications).

    // DELTAC applies adjustments to these originals, not WCVTP-modified values.

    pub(crate) cvt_original: Vec<i32>,

    // Accumulated DELTAC adjustments per CVT entry. Multiple DELTACs

    // targeting the same CVT at the same ppem accumulate their deltas.

    cvt_deltac_accum: Vec<i32>,

    // Storage area

    pub(crate) storage: Vec<i32>,

    // Function/instruction definitions

    pub(crate) fdefs: Vec<Option<FuncDef>>,

    pub(crate) idefs: Vec<Option<FuncDef>>,

    // Graphics state

    pub(crate) gs: GraphicsState,

    pub(crate) default_gs: GraphicsState,

    // Zones: 0 = twilight, 1 = glyph

    pub(crate) zones: [Zone; 2],

    // Font metrics

    pub(crate) ppem: u16,

    pub(crate) point_size: i32, // F26Dot6

    pub(crate) units_per_em: u16,

    pub(crate) scale: i64, // 16.16 fixed-point

    // Execution state

    instruction_count: u64,

    call_depth: u32,

    /// When true, dump every instruction to stderr (for debugging)

    pub trace_mode: bool,

    /// When true, log move_point calls on glyph zone to stderr

    pub debug_trace_points: bool,

    // ── Hinting mode flags (toggle to find correct behavior) ────────

    /// Flag A: Reset X coordinates to original after glyph program.

    /// Matches FreeType v40 / Chrome which only applies Y-axis hinting.

    /// Without this: full X+Y hinting (v35 mode), causes SHPIX spacing issues.

    /// With this: Y-only hinting, but curves that depend on X/Y coordination

    /// (e.g., 'u' bottom curve at ppem=20) may distort.

    pub suppress_x_axis: bool,

    /// Flag B: Snapshot Y after IUP[Y], discard post-IUP Y modifications.

    /// Some glyph programs modify Y after IUP via function calls (e.g.,

    /// 'o' at ppem=12: pt5 moves from 150→77). FreeType v40 may suppress these.

    /// Without this: post-IUP moves apply, causing diamond shapes at small ppem.

    /// With this: clean IUP interpolation preserved, but some legitimate

    /// post-IUP adjustments are also discarded.

    pub snapshot_iup_y: bool,

    /// Flag C: Use orig_dist sign for minimum_distance when dist rounds to zero.

    /// Without this: small negative distances get +min_dist (wrong direction).

    /// With this: preserves original direction, matching FreeType behavior.

    pub fix_min_distance_sign: bool,

    /// Snapshot of Y coordinates taken right after IUP[Y] runs.

    iup_y_snapshot: Option<Vec<i32>>,

}

impl Interpreter {

    /// Create a new interpreter from maxp table values.

        // FreeType sizes the stack to maxStackElements + 32 so under-declared

        // fonts (whose real high-water mark exceeds maxp) don't lose all hinting.

    /// Returns the current CVT values (F26Dot6 stored as i32).

    /// Returns the max stack size.

    /// Returns the graphics state (for debugging).

    /// Returns the storage area size.

    /// Read a storage area value (for debugging).

    /// Returns the number of function definitions.

    /// Returns the number of twilight zone points.

    /// Returns the ppem value.

    /// Returns the scale value (16.16 fixed-point).

    /// Returns units_per_em.

    /// Execute the font program (`fpgm`) to populate function definitions.

    /// Set the ppem size and execute the prep program.

        // Note: storage is NOT cleared between prep runs.

        // The prep program is responsible for setting all values it needs.

        // Save the modified graphics state as the default for glyph programs

    /// Scale CVT values from FUnits to F26Dot6 pixels.

        // Save original scaled CVT values. DELTAC applies adjustments

        // to these originals, not to WCVTP-modified values. Without this,

        // the prep's WCVTP rounds CVT[0] from 1422→1408, then DELTAC(-40)

        // gives 1368 (rounds to 1344=21px). With originals, DELTAC(-40)

        // applies to 1422 giving 1382 (rounds to 1408=22px, correct).

    /// Hint a glyph outline by executing its bytecode instructions.

    ///

    /// `points` are pre-scaled to F26Dot6 coordinates.

    /// `on_curve` flags indicate whether each point is on-curve.

    /// `contour_ends` gives the index of the last point in each contour.

    /// `instructions` is the per-glyph bytecode from the glyf table.

    ///

    /// After execution, the hinted point positions can be read from

    /// `self.zones[1].current`.

        // Set up the glyph zone with empty orus (no unscaled data)

    /// Hint a glyph with optional unscaled original coordinates (orus).

    ///

    /// If `orus` is provided, IUP interpolation uses these exact integer

    /// coordinates instead of the scaled F26Dot6 `points`. This matches

    /// FreeType's approach and avoids ±1 F26Dot6 rounding errors in IUP.

        // Set up the glyph zone

            // Store unscaled coordinates if provided, otherwise use scaled

            } else {

            };

        }

        // Reset graphics state to defaults (set by prep), then override

        // per TrueType spec: projection/freedom vectors reset to x-axis,

        // reference points to 0, loop to 1, zone pointers to 1.

        // FreeType TT_Run_Context resets round_state to RTG (1) before every

        // glyph, so a non-grid round mode left active by prep does not leak in.

        // v40 backward compatibility: undo X-axis movements AND post-IUP

        // Y-axis modifications.

        //

        // FreeType v40 (DEFAULT mode) and Chrome/Core Text on macOS:

        // - Suppress all X-axis grid-fitting (subpixel rendering handles X)

        // - After IUP[Y], some glyph programs apply post-IUP function calls

        //   that modify Y coordinates (e.g., Times New Roman 'o' at ppem=12

        //   moves pt5.y from 150→77 via a called function). FreeType v40

        //   suppresses these post-IUP modifications.

        //

        // We handle this by saving Y values right after IUP[Y] runs

        // (stored in `iup_y_snapshot`) and restoring them after execution.

        // Flag A: suppress X-axis movements

        // Flag B: restore Y from IUP snapshot (discard post-IUP Y mods)

    // ── Core execution loop ──────────────────────────────────────────

        }

            // ── Vector setting ───────────────────────────────────

                // SPVTL[a] - set projection vector to line

            }

                // SFVTL[a] - set freedom vector to line

            }

            0x0A => {

                // SPVFS - set projection vector from stack

            }

            0x0B => {

                // SFVFS - set freedom vector from stack

            }

            0x0C => {

                // GPV - get projection vector

            }

            0x0D => {

                // GFV - get freedom vector

            }

            0x0F => {

                // ISECT - move point to intersection

            }

            // ── Reference point / zone setting ───────────────────

            0x10 => {

                // SRP0

            }

            0x11 => {

                // SRP1

            }

            0x12 => {

                // SRP2

            }

            0x13 => {

                // SZP0

            }

            0x14 => {

                // SZP1

            }

            0x15 => {

                // SZP2

            }

            0x16 => {

                // SZPS - set all zone pointers

            }

            0x17 => {

                // SLOOP

            }

            // ── Rounding mode ────────────────────────────────────

            // ── Distances ────────────────────────────────────────

            0x1A => {

                // SMD - set minimum distance

            }

            // ── Control flow ─────────────────────────────────────

            0x1B => {

                // ELSE - skip to EIF

            }

            0x1C => {

                // JMPR - jump relative

                // offset is relative to the JMPR opcode position (*ip - 1)

            }

            0x1D => {

                // SCVTCI - set CVT cut-in

            }

            0x1E => {

                // SSWCI - set single width cut-in

            }

            0x1F => {

                // SSW - set single width value (FUnits -> F26Dot6)

            }

            // ── Stack manipulation ───────────────────────────────

            0x20 => {

                // DUP

            }

            0x21 => {

                // POP

            }

            0x23 => {

                // SWAP

            }

            0x24 => {

                // DEPTH

            }

            0x25 => {

                // CINDEX - copy indexed element

            }

            0x26 => {

                // MINDEX - move indexed element to top

            }

            // ── Point alignment ──────────────────────────────────

            0x27 => {

                // ALIGNPTS

            }

            0x29 => {

                // UTP - untouch point

                    // Clear touched flags based on freedom vector

            }

            // ── Function calls ───────────────────────────────────

            0x2A => {

                // LOOPCALL

                    .bytecode

                }

            }

            0x2B => {

                // CALL

                    .bytecode

            }

            0x2C => {

                // FDEF - function definition

                // Scan forward to find ENDF (0x2D), handling nested FDEF/ENDF

                // ip now points past ENDF

            }

            0x2D => {

                // ENDF - end of function

                // In normal execution flow (inside CALL), this returns from execute()

            }

            // ── Point movement ───────────────────────────────────

                // MDAP[r] - move direct absolute point

            }

                // IUP[a] - interpolate untouched points

                // In v40 mode, snapshot Y values right after IUP[Y] runs

                // so post-IUP function calls can't modify them.

                    );

            }

                // SHP[a] - shift point

                // SHP[0] (0x32) uses rp2/zp1, SHP[1] (0x33) uses rp1/zp0

            }

                // SHC[a] - shift contour

                // SHC[0] (0x34) uses rp2/zp1, SHC[1] (0x35) uses rp1/zp0

            }

                // SHZ[a] - shift zone

                // SHZ[0] (0x36) uses rp2/zp1, SHZ[1] (0x37) uses rp1/zp0

            }

            0x38 => {

                // SHPIX - shift point by pixel amount

            }

            0x39 => {

                // IP - interpolate point

            }

                // MSIRP[a] - move stack indirect relative point

            }

            0x3C => {

                // ALIGNRP - align relative point

            }

                // MIAP[r] - move indirect absolute point

            }

            // ── Push instructions ────────────────────────────────

            0x40 => {

                // NPUSHB - push n bytes

                }

            }

            0x41 => {

                // NPUSHW - push n words

                    // Cast high byte to i8 for proper sign extension.

                }

            }

            // ── Storage / CVT ────────────────────────────────────

            0x42 => {

                // WS - write storage

                // Dynamically grow storage if needed (fonts may exceed maxp limits)

            }

            0x43 => {

                // RS - read storage

                // Dynamically grow storage if needed (reads default to 0)

            }

            0x44 => {

                // WCVTP - write CVT in pixel units (F26Dot6)

                    // Bounds-check like WS/RS: an out-of-range (negative/huge)

                    // index must not trigger a multi-GB resize/OOM.

            }

            0x45 => {

                // RCVT - read CVT

            }

                // GC[a] - get coordinate (0=current, 1=original)

            }

            0x48 => {

                // SCFS - set coordinate from stack

            }

                // MD[a] - measure distance

                // 0x49 = MD[0]: use current (grid-fitted) positions

                // 0x4A = MD[1]: use original (unhinted) positions

                // 0x49 = MD[0]: use current (grid-fitted) positions

                // 0x4A = MD[1]: use original (unhinted) positions

            }

            0x4B => {

                // MPPEM - measure pixels per em

            }

            0x4C => {

                // MPS - measure point size (F26Dot6)

            }

            // ── Boolean / flip ───────────────────────────────────

            // ── Comparison ───────────────────────────────────────

            0x50 => {

                // LT

            }

            0x51 => {

                // LTEQ

            }

            0x52 => {

                // GT

            }

            0x53 => {

                // GTEQ

            }

            0x54 => {

                // EQ

            }

            0x55 => {

                // NEQ

            }

            0x56 => {

                // ODD

            }

            0x57 => {

                // EVEN

            }

            // ── IF / ELSE / EIF ──────────────────────────────────

            0x58 => {

                // IF

            }

            // ── Logic ────────────────────────────────────────────

            0x5A => {

                // AND

            }

            0x5B => {

                // OR

            }

            0x5C => {

                // NOT

            }

            // ── Delta instructions ───────────────────────────────

            0x5E => {

                // SDB - set delta base

            }

            0x5F => {

                // SDS - set delta shift

            }

            // ── Arithmetic ───────────────────────────────────────

            0x60 => {

                // ADD

            }

            0x61 => {

                // SUB

            }

            0x62 => {

                // DIV

                // F26Dot6 division: a * 64 / b with FreeType-compatible rounding

            }

            0x63 => {

                // MUL

                // F26Dot6 multiplication: a * b / 64 with FreeType-compatible rounding

            }

            0x64 => {

                // ABS

            }

            0x65 => {

                // NEG

            }

            0x66 => {

                // FLOOR

            }

            0x67 => {

                // CEILING

            }

            // ── ROUND / NROUND ───────────────────────────────────

                // ROUND[ab] - round value

            }

            // ── More CVT / Delta ─────────────────────────────────

            0x70 => {

                // WCVTF - write CVT in FUnits

            }

            // ── Super rounding ───────────────────────────────────

            0x76 => {

                // SROUND

            }

            0x77 => {

                // S45ROUND

            }

            // ── Conditional jumps ────────────────────────────────

            0x78 => {

                // JROT - jump relative on true

                    // offset is relative to the JROT opcode position (*ip - 1)

            }

            0x79 => {

                // JROF - jump relative on false

                    // offset is relative to the JROF opcode position (*ip - 1)

            }

            0x7E => {

                // SANGW (obsolete) - no-op

            }

            0x7F => {

                // AA (obsolete) - no-op

            }

            // ── Flip instructions ────────────────────────────────

            0x80 => {

                // FLIPPT

            }

            0x81 => {

                // FLIPRGON

                // Clamp the range to the glyph zone so a huge/negative index

                // (e.g. -1 -> usize::MAX) does not spin an unbounded loop.

            }

            0x82 => {

                // FLIPRGOFF

            }

            0x85 => {

                // SCANCTRL

            }