###
post: Reading a MATPOWER case file
agent: claude

A MATPOWER case file (MATPOWER's `caseformat`, version 2, and the older
version 1 of its test cases) is a MATLAB function that sets the system base
`baseMVA` and three matrices, one row per bus, generator and branch.
`read_case(path)` reads those four and ignores the rest (`gencost`, area
data, the function line, comments after `%`).

The column numbers below are MATPOWER's (idx_bus, idx_gen, idx_brch),
counted from 0. A power flow reads the input columns and fills the result
columns: bus voltages, generator outputs and, in four extra branch columns,
the power entering each end of a branch.
###

record Case {
    base_mva: Num
    bus: Arr
    gen: Arr
    branch: Arr
}

#: bus columns
BUS_I: Int = 0
BUS_TYPE: Int = 1
PD: Int = 2
QD: Int = 3
GS: Int = 4
BS: Int = 5
VM: Int = 7
VA: Int = 8

#: generator columns
GEN_BUS: Int = 0
PG: Int = 1
QG: Int = 2
QMAX: Int = 3
QMIN: Int = 4
VG: Int = 5
GEN_STATUS: Int = 7

#: branch columns (the last four are results)
F_BUS: Int = 0
T_BUS: Int = 1
BR_R: Int = 2
BR_X: Int = 3
BR_B: Int = 4
TAP: Int = 8
SHIFT: Int = 9
BR_STATUS: Int = 10
PF: Int = 13
QF: Int = 14
PT: Int = 15
QT: Int = 16
BRANCH_COLS: Int = 17

#: bus types
PQ: Int = 1
PV: Int = 2
REF: Int = 3
NONE: Int = 4

#| The case in a MATPOWER .m file: baseMVA and the bus, gen and branch
#| matrices, as written (external bus numbers, every row kept).
def read_case(path: Str) -> Case {
    lines = read_lines(path)
    base = 0.0
    for line in lines {
        s = strip(_uncomment(line))
        if startswith(s, "mpc.baseMVA") or startswith(s, "baseMVA") {
            base = float(strip(replace(split(s, "=")[1], ";", "")))
        }
    }
    if base <= 0.0 {
        stop(f"read_case: {path} sets no baseMVA")
    }
    return Case { base_mva: base, bus: _matrix(lines, "bus", path), gen: _matrix(lines, "gen", path),
                  branch: _matrix(lines, "branch", path) }
}

def _uncomment(line: Str) -> Str {
    k = find(line, "%")
    if k >= 0 {
        return line[:k]
    }
    return line
}

#| The rows between `mpc.<name> = [` (or `<name> = [`) and `];`.
def _matrix(lines: [Str], name: Str, path: Str) -> Arr {
    M = []
    inside = false
    found = false
    for line in lines {
        s = strip(_uncomment(line))
        if not inside {
            head = strip(split(s, "=")[0]) if "=" in s else ""
            if (head == "mpc." + name or head == name) and "[" in s {
                inside = true
                found = true
                s = strip(split(s, "[")[1])
            }
            else {
                continue
            }
        }
        done = "]" in s
        if done {
            s = split(s, "]")[0]
        }
        for part in split(s, ";") {
            fields = split(strip(part))
            if len(fields) > 0 {
                M = append(M, [float(f) for f in fields])
            }
        }
        if done {
            break
        }
    }
    if not found {
        stop(f"read_case: {path} has no {name} matrix")
    }
    return M
}

test "case9: baseMVA, 9 buses, 3 generators, 9 branches" {
    c = read_case("lib/power/cases/case9.m")
    assert_near(c.base_mva, 100.0, 0.0)
    assert_allclose(shape(c.bus), [9.0, 13.0], 0.0)
    assert_allclose(shape(c.gen), [3.0, 21.0], 0.0)
    assert_allclose(shape(c.branch), [9.0, 13.0], 0.0)
    assert_near(c.bus[4, PD], 90.0, 0.0)
    assert_near(c.branch[1, BR_B], 0.158, 0.0)
}

test "a version 1 case (MATPOWER's t_case9_pf) reads the same way" {
    c = read_case("lib/power/cases/t_case9_pf.m")
    assert_allclose(shape(c.bus), [9.0, 13.0], 0.0)
    assert_near(c.bus[2, BUS_I], 30.0, 0.0)
    assert_allclose(shape(c.gen), [3.0, 10.0], 0.0)
}

# SPDX-License-Identifier: MIT OR Apache-2.0
# SPDX-FileCopyrightText: 2026 The Viv authors