r"""
The 1953 Stockholm convention: electrode potentials are reduction potentials
==============================================================================

Before IUPAC's 1953 Stockholm meeting, one tradition tabulated
*oxidation* potentials and another *reduction* potentials, so the same
couple appeared with opposite signs in different books. This example
shows both conventions for the table in
:data:`~chemistrykit.electrochem.systems.standard_potentials.STANDARD_REDUCTION_POTENTIALS`
(which follows Stockholm), and shows that the cathode-minus-anode rule of
:func:`~chemistrykit.electrochem.systems.standard_potentials.cell_potential`
only gives the right cell voltage and spontaneity when both half-reactions
use the agreed reduction convention.
"""

# %%
import matplotlib.pyplot as plt
import numpy as np

from chemistrykit.electrochem.systems.standard_potentials import STANDARD_REDUCTION_POTENTIALS as T
from chemistrykit.electrochem.systems.standard_potentials import cell_potential, is_spontaneous

# %%
# Correct usage: both values are Stockholm reduction potentials.
E_ok = cell_potential(T["Ag+/Ag"], T["Cu2+/Cu"])
print(f"Ag+/Ag cathode, Cu anode (both reduction potentials): E = {E_ok:+.2f} V, spontaneous = {is_spontaneous(E_ok)}")

# %%
# The historical pitfall: taking the anode value from an oxidation-potential
# table (sign flipped) and subtracting it gives nonsense.
E_mixed = T["Ag+/Ag"].E_standard - (-T["Cu2+/Cu"].E_standard)
print(f"Same cell with a mixed-convention anode value: E = {E_mixed:+.2f} V (wrong; measured 0.46 V)")

# %%
# The whole table in both conventions: the oxidation-potential column is
# the mirror image of the Stockholm (reduction) column.
names = list(T)
E_red = np.array([T[name].E_standard for name in names])
order = np.argsort(E_red)
y = np.arange(len(names))

fig, ax = plt.subplots(figsize=(7, 7))
ax.barh(y - 0.2, E_red[order], height=0.4, color="steelblue", label="Reduction potential (Stockholm, 1953)")
ax.barh(y + 0.2, -E_red[order], height=0.4, color="lightgray", label="Oxidation potential (older convention)")
ax.set_yticks(y)
ax.set_yticklabels([names[i] for i in order], fontsize=8)
ax.axvline(0.0, color="black", linewidth=0.8)
ax.set_xlabel("Tabulated potential (V vs. SHE)")
ax.set_title("One couple, two historical signs")
ax.legend(fontsize=8, loc="lower right")
fig.tight_layout()
plt.show()