const std = @import("std");

/// Extract a string field value from a JSON blob (minimal parser — no allocations).

pub fn parseStringField(json: []const u8, key: []const u8) ?[]const u8 {

var needle_buf: [256]u8 = undefined;

const quoted_key = std.fmt.bufPrint(&needle_buf, "\"{s}\"", .{key}) catch return null;

const key_pos = std.mem.indexOf(u8, json, quoted_key) orelse return null;

const after_key = json[key_pos + quoted_key.len ..];

var i: usize = 0;

while (i < after_key.len and (after_key[i] == ' ' or after_key[i] == ':' or after_key[i] == '\t' or after_key[i] == '\n')) : (i += 1) {}

if (i >= after_key.len or after_key[i] != '"') return null;

i += 1;

const start = i;

while (i < after_key.len) : (i += 1) {

if (after_key[i] == '\\' and i + 1 < after_key.len) {

i += 1;

continue;

}

if (after_key[i] == '"') return after_key[start..i];

}

return null;

}

/// Extract a boolean field value from a JSON blob.

pub fn parseBoolField(json: []const u8, key: []const u8) ?bool {

var needle_buf: [256]u8 = undefined;

const quoted_key = std.fmt.bufPrint(&needle_buf, "\"{s}\"", .{key}) catch return null;

const key_pos = std.mem.indexOf(u8, json, quoted_key) orelse return null;

const after_key = json[key_pos + quoted_key.len ..];

var i: usize = 0;

while (i < after_key.len and (after_key[i] == ' ' or after_key[i] == ':' or after_key[i] == '\t' or after_key[i] == '\n')) : (i += 1) {}

if (i + 4 <= after_key.len and std.mem.eql(u8, after_key[i..][0..4], "true")) return true;

if (i + 5 <= after_key.len and std.mem.eql(u8, after_key[i..][0..5], "false")) return false;

return null;

}

/// Extract an integer field value from a JSON blob.

pub fn parseIntField(json: []const u8, key: []const u8) ?i64 {

var needle_buf: [256]u8 = undefined;

const quoted_key = std.fmt.bufPrint(&needle_buf, "\"{s}\"", .{key}) catch return null;

const key_pos = std.mem.indexOf(u8, json, quoted_key) orelse return null;

const after_key = json[key_pos + quoted_key.len ..];

var i: usize = 0;

while (i < after_key.len and (after_key[i] == ' ' or after_key[i] == ':' or after_key[i] == '\t' or after_key[i] == '\n')) : (i += 1) {}

const start = i;

if (i < after_key.len and after_key[i] == '-') i += 1;

while (i < after_key.len and after_key[i] >= '0' and after_key[i] <= '9') : (i += 1) {}

if (i == start) return null;

return std.fmt.parseInt(i64, after_key[start..i], 10) catch null;

}

/// Extract an unsigned integer field value from a JSON blob.

pub fn parseUintField(json: []const u8, key: []const u8) ?u64 {

var needle_buf: [256]u8 = undefined;

const quoted_key = std.fmt.bufPrint(&needle_buf, "\"{s}\"", .{key}) catch return null;

const key_pos = std.mem.indexOf(u8, json, quoted_key) orelse return null;

const after_key = json[key_pos + quoted_key.len ..];

var i: usize = 0;

while (i < after_key.len and (after_key[i] == ' ' or after_key[i] == ':' or after_key[i] == '\t' or after_key[i] == '\n')) : (i += 1) {}

const start = i;

while (i < after_key.len and after_key[i] >= '0' and after_key[i] <= '9') : (i += 1) {}

if (i == start) return null;

return std.fmt.parseInt(u64, after_key[start..i], 10) catch null;

}

test "json_miniparse parseStringField basic" {

const json = "{\"command\": \"echo hello\", \"other\": \"val\"}";

const val = parseStringField(json, "command");

try std.testing.expect(val != null);

try std.testing.expectEqualStrings("echo hello", val.?);

}

test "json_miniparse parseBoolField values" {

try std.testing.expectEqual(true, parseBoolField("{\"enabled\": true}", "enabled").?);

try std.testing.expectEqual(false, parseBoolField("{\"enabled\": false}", "enabled").?);

}

test "json_miniparse parseIntField supports signed numbers" {

try std.testing.expectEqual(@as(i64, 42), parseIntField("{\"n\": 42}", "n").?);

try std.testing.expectEqual(@as(i64, -7), parseIntField("{\"n\": -7}", "n").?);

}

test "json_miniparse parseUintField supports positive numbers" {

try std.testing.expectEqual(@as(u64, 42), parseUintField("{\"n\": 42}", "n").?);

}

test "json_miniparse missing fields return null" {

try std.testing.expect(parseStringField("{\"x\":1}", "name") == null);

try std.testing.expect(parseBoolField("{\"x\":1}", "enabled") == null);

try std.testing.expect(parseIntField("{\"x\":1}", "n") == null);

try std.testing.expect(parseUintField("{\"x\":1}", "n") == null);

}