// Gap buffer
// SPDX-FileCopyrightText: 2025 Nguyễn Gia Phong
// SPDX-License-Identifier: GPL-3.0-or-later

const assert = std.debug.assert;
const eql = std.meta.eql;
const std = @import("std");

const Input = tree_sitter.Input;
const Parser = tree_sitter.Parser;
const Point = tree_sitter.Point;
const Tree = tree_sitter.Tree;
const tree_sitter = @import("tree-sitter");

const Grapheme = Graphemes.Grapheme;
const Graphemes = vaxis.Graphemes;
const vaxis = @import("vaxis");

const janet = zsanett.janet;
const zsanett = @import("zsanett");

const Selection = @import("Selection.zig");
const languages = @import("languages");
const graphemes = &@import("main.zig").graphemes;

const initial_gap_size = std.atomic.cache_line;

const Buffer = @This();
/// File content with gap, owned by Janet runtime.
data: []const u8,
file: []const u8,
gap_position: u32 = 0,
gap_size: u32 = initial_gap_size,
parser: *Parser,
tree: *Tree, // TODO: polyglot
scroll_row: u32 = 0,
selection: Selection,
paste_direction: enum { before, after } = .before,

fn read(payload: ?*anyopaque, byte_index: u32, _: Point,
        bytes_read: *u32) callconv(.C) [*c]const u8 {
    const buffer: *Buffer = @alignCast(@ptrCast(payload.?));
    if (byte_index < buffer.gap_position) {
        bytes_read.* = @intCast(buffer.gap_position - byte_index);
        return buffer.data[byte_index..buffer.gap_position].ptr;
    }
    const index_with_gap = byte_index + buffer.gap_size;
    if (index_with_gap < buffer.data.len) {
        bytes_read.* = @intCast(buffer.data.len - index_with_gap);
        return buffer.data[index_with_gap..].ptr;
    } else {
        bytes_read.* = 0;
        return "";
    }
}

pub fn open(text: []const u8, file: []const u8) !Buffer {
    const data = gap: {
        const unsafe_ptr: *anyopaque = @constCast(@ptrCast(text.ptr));
        const n: i32 = @intCast(text.len);
        const buffer = janet.pointerBufferUnsafe(unsafe_ptr, n, n);
        const capacity: usize = @intCast(n + initial_gap_size);
        if (janet.realloc(buffer.*.data, capacity)) |data| {
            janet.gcpressure(initial_gap_size);
            buffer.*.data = @ptrCast(data);
            buffer.*.capacity = @intCast(capacity);
            buffer.*.count = buffer.*.capacity;
            // TODO: use @memmove in Zig 0.15
            var i = capacity;
            while (i >= initial_gap_size) : (i -= 1)
                buffer.*.data[i] = buffer.*.data[i - initial_gap_size];
            break :gap buffer.*.data[0..capacity];
        } else return error.OutOfMemory;
    };

    const parser = Parser.create();
    errdefer parser.destroy();
    const language = languages.c();
    errdefer language.destroy();
    try parser.setLanguage(language);
    var result = Buffer{
        .data = data,
        .file = file,
        .parser = parser,
        .tree = undefined,
        .selection = undefined,
    };
    result.tree = parser.parse(.{
        .payload = &result,
        .read = Buffer.read,
    }, null).?;
    const span0 = Selection.Unit{ .span = .{ .tree = result.tree } };
    result.selection = .{ .head = span0, .tail = span0 };
    return result;
}

pub fn close(buffer: Buffer) void {
    buffer.tree.getLanguage().destroy();
    buffer.tree.destroy();
    buffer.parser.destroy();
}

pub fn length(buffer: Buffer) u32 {
    return @intCast(buffer.data.len - buffer.gap_size);
}

pub fn graphemeAt(buffer: Buffer, n: u32) Grapheme {
    const text = if (n < buffer.gap_position)
        buffer.data[n..buffer.gap_position]
    else
        buffer.data[buffer.gap_size..][n..];
    var iterator = graphemes.iterator(text);
    return .{ .offset = n, .len = iterator.peek().?.len };
}

pub fn graphemeBefore(buffer: Buffer, n: u32) ?Grapheme {
    if (n == 0)
        return null;
    const text = if (n <= buffer.gap_position)
        buffer.data[0..n]
    else
        buffer.data[buffer.gap_size..][buffer.gap_position..n];
    var iterator = graphemes.reverseIterator(text);
    const len = iterator.peek().?.len;
    return .{ .offset = n - len, .len = len };
}

fn skipLines(text: []const u8, from: u32, n: u32) union(enum) {
    done: u32,
    left: u32,
} {
    if (n == 0)
        return .{ .done = from };
    var lines: u32 = 0;
    for (text[from..], 1..) |c, i|
        if (c == '\n') {
            lines += 1;
            if (lines == n)
                return .{ .done = @intCast(from + i) };
        };
    return .{ .left = n - lines };
}

pub fn iterate(buffer: Buffer) struct {
    const Iterator = @This();
    graphemes_iterator: Graphemes.Iterator,
    data: []const u8,
    offset: u32,
    before_gap: bool,
    gap_start: u32,
    gap_end: u32,

    pub fn next(iterator: *Iterator) ?Grapheme {
        if (iterator.graphemes_iterator.next()) |grapheme| {
            return .{
                .offset = grapheme.offset + iterator.offset,
                .len = grapheme.len,
            };
        } else if (iterator.before_gap) {
            const buffer_after_gap = iterator.data[iterator.gap_end..];
            iterator.graphemes_iterator = graphemes.iterator(buffer_after_gap);
            iterator.offset = iterator.gap_start;
            iterator.before_gap = false;
            return iterator.next();
        } else return null;
    }
} {
    const point = Point{ .row = buffer.scroll_row, .column = 0 };
    const root_node = buffer.tree.rootNode();
    const root_start = root_node.startPoint();
    const start = if (root_start.row < point.row
                      or eql(root_start, point)) skip: {
        const node = root_node.descendantForPointRange(point, point).?;
        const start_point = node.startPoint();
        const start_byte = node.startByte();
        if (eql(start_point, point))
            break :skip start_byte;
        assert(start_point.row < point.row);
        break :skip if (start_byte >= buffer.gap_position)
            skipLines(buffer.data[buffer.gap_size..],
                      start_byte, point.row - start_point.row).done
        else switch (skipLines(buffer.data[0..buffer.gap_position],
                               start_byte, point.row - start_point.row)) {
            .done => |offset| offset,
            .left => |left| skipLines(buffer.data[buffer.gap_size..],
                                      buffer.gap_position, left).done,
        };
    } else switch (skipLines(buffer.data[0..buffer.gap_position], 0,
                             point.row)) {
        .done => |offset| offset,
        .left => |left| skipLines(buffer.data[buffer.gap_size..],
                                  buffer.gap_position, left).done,
    };
    if (start < buffer.gap_position) {
        const buffer_before_gap = buffer.data[start..buffer.gap_position];
        return .{
            .graphemes_iterator = graphemes.iterator(buffer_before_gap),
            .data = buffer.data,
            .offset = start,
            .before_gap = true,
            .gap_start = buffer.gap_position,
            .gap_end = buffer.gap_position + buffer.gap_size,
        };
    }
    const offset = start + buffer.gap_size;
    return .{
        .graphemes_iterator = graphemes.iterator(buffer.data[offset..]),
        .data = undefined,
        .offset = start,
        .before_gap = false,
        .gap_start = undefined,
        .gap_end = undefined,
    };
}

pub fn bytes(buffer: Buffer, grapheme: Grapheme) []const u8 {
    if (grapheme.offset < buffer.gap_position)
        return grapheme.bytes(buffer.data);
    const start = grapheme.offset + buffer.gap_size;
    const end = start + grapheme.len;
    return buffer.data[start..end];
}

pub fn selectedBytes(buffer: Buffer) []const u8 {
    const start = buffer.selection.startByte();
    const end = buffer.selection.endByte();
    if (end <= buffer.gap_position)
        return buffer.data[start..end];
    if (start >= buffer.gap_position)
        return buffer.data[buffer.gap_size..][start..end];
    unreachable;
}

pub fn paste(buffer: Buffer, data: []const u8) Buffer {
    _ = data;
    return buffer;
}